This invention relates to a shank-end tool with permanently attached wing-like inserts for the milling-type machining of chipless materials for the manufacture of molds, especially heat-resistant casting molds for producing metal castings.
Primarily sand molds that are made with the help of patterns are used in practice to produce metal castings. Since it is costly to make patterns, there has long been a need to make casting molds by direct machining of heat-resistant molding compositions for small and medium-sized runs.
In DE PS 26 05 687 C3, a cutting and milling tool is used to hollow out a mold cavity to produce sand molds, which is used in active combination with a duplicating miller. The milling tool has a knife assembly with a cutter that conforms essentially to an inverted T-shape and is fastened to an arm that rotates around an axis of rotation. The cutter is interchangeable, it is curved on the outside to smooth the mold surface according to the inside diameter of the casting mold to be produced, and viewed in the direction of rotation it is shaped on the forward edge so that a cutting edge is formed. A hardenable green sand with low strength of 2–5 kg/cm2 compacted in a molding box is hollowed out with the cutter before the final strength of the molding sand after hardening is reached. This is to prevent fast wear of the cutting edge. The method is relatively difficult to perform because the proper time for the machining has to be provided for during the hardening of the mold. Otherwise the mold becomes dirty with low-strength molding sand, or the cutter quickly becomes unusable with high-strength sand. Furthermore, the milling tools can be used only to make rotationally symmetrical parts.
On the other hand, it was proposed in DD 275 419 A1 to work out a casting mold from a single block of mold material with tools that have no cutter geometry. To produce a cavity in a block of mold material, a device is used that includes a rod-shaped driver driven around an axis on which at least two non-rigid or semi-rigid carriers variable in length are guided. Active machining units are fastened to these carriers and are positioned at identical angular graduations on the driver to avoid imbalance. Flat parts such as triangular plates, stars, or the like, or balls or squares or others with or without edges can be used as active machining units, for example. Cables, wire cables, sheet metal strips, chains, or the like can be used as non-rigid or semi-rigid carriers, and are provided with additional guard elements to protect against the wear caused by the eroded sand mold material.
To increase excavating capacity, it is necessary during the machining to achieve the highest possible stiffness of the carriers by arranging the machining units to be movable and having them braced against one another. The device can be run under computer control on the arm of a robot. In the same way, it is also possible to control the device by a CNC machine. To improve the surface of the castings, the inner surfaces enclosing the cavity space are sprayed in a concluding step with a smoothing agent, which has to be distributed evenly over the surface. In this case also, it is a drawback that essentially only molds that differ only roughly from rotationally symmetrical parts can be made. The low surface quality of the castings produced with the casting molds is a drawback that can be attributed to the more or less beating action of the tools.
Shank-end millers that have a circular contour are customary for the production of casting molds. The shank-end miller described in DE 197 21 900 A1 has a cutting plate on the free end that is fastened to the shank with tightening screws. The shank has a plate seat with a threaded bore, with the cutting plate being provided with a drilled hole. However, such fastening runs into problems when the dimensions of the cutting plates are smaller than a minimum size. Therefore, it is difficult to loosen the cutting plate or to fasten it satisfactorily. It is also a drawback that the cutting plate is exposed to high wear from chipless materials. This makes it necessary to change tools constantly, which is associated with correspondingly high cost.
To reduce the tool cost occurring from high wear, an economically manufactured milling tool was proposed in DE 3914074 A1 that has a cylindrical shank and a flat cutter support. The cutter support is provided with cutting edges at its edges farthest from the axis of the shank. There are additional frontal cutting plates on the face of the cutter support. The shank is designed as a borer at one end so that the miller can function as a face mill. The cutters are positioned at the radially terminal outer edges of the cutter support relative to the axis of the shank. The cross section of the milling tool shows an S-shaped profile with the cutting edge pointing in the cutting direction. For this reason the previously described miller can be used only for chip-forming materials. Use is not possible for chipless materials.
Foundry sands containing binders bring about a severe degree of wear of the tool cutters, which is caused by wear of the cutters at the cutting edges and frictional wear on the open surfaces. For this reason there is cutting action only with new tools, and there is thus a time limit for it. The cutter wear is manifested as rounding of the forward edge of the tool, which causes additional frictional wear in the area behind the cutting edge. This frictional wear increasingly erodes the outer surfaces and deforms the tool increasingly toward the rear opposite to the direction of rotation. The energy corresponding to the friction is converted into heat, which can lead to heating of the tool and to more rapidly increasing wear.
The problem underlying this invention is to design a shank-end tool for milling-type machining that is simple and economical to manufacture, in such a way that it remains functional with unavoidable frictional wear and with increasing erosion. The machining action should be retained for a lengthy period of time. The losses from friction should be lowered.